This invention relates to a process for treating copper and, more particularly, to a process for applying a metal to at least one side of a copper foil.
Copper foil is used in the production of printed circuit boards. In the production of printed circuit boards, it is generally necessary to bond a copper foil to a dielectric substrate to provide the foil with dimensional and structural stability. Although an excellent electronic conductor, there are problems inherent with the use of copper foil. For example, copper is easily oxidized and corroded, and copper itself, whether plated or rolled, does not adhere well to such substrates. Copper is also known to accelerate or catalyze the decomposition of the dielectric substrates. For these reasons, copper foil is typically sold with one or more protective layers applied to its surface.
It is known that a thin, chromium layer deposited onto copper foil has many applications for printed circuit boards. There are two ways to deposit the thin chromium layer onto a copper surface. One is by an electrodeposition process, and the other is by a vacuum deposition process.
The electrodeposition process has several disadvantages. Foremost, the process uses environmentally hazardous material that is difficult and costly to handle and dispose of. Further, this type of process is inexact and inefficient.
With respect to the vacuum deposition process, in order to insure a satisfactory adhesion between the applied chromium and copper, an extensive and rigorous pretreatment of the copper is required to remove copper oxide from the surface thereof prior to the vacuum deposition of the chromium.
The present invention overcomes these and other problems and provides a method of forming a metal coated copper by a vacuum deposition process that does not require an extensive rigorous pre-treatment process.
In accordance with a preferred embodiment of the present invention, there is provided a method of applying a metal onto a copper layer, comprising the steps of stabilizing a surface of a copper layer by applying a stabilization layer thereto, the stabilization layer comprised of zinc oxide, chromium oxide, nickel oxide or a combination thereof and having a thickness of between about 5 xc3x85 and about 70 xc3x85, and vapor depositing a metal selected from the group consisting of aluminum, nickel, chromium, copper, iron, indium, zinc, tantalum, tin, vanadium, tungsten, zirconium, molybdenum and alloys thereof onto the stabilized surface of the copper layer. One specific alloy contemplated herein is nickel-chromium alloy.
In accordance with another aspect of the present invention, there is provided a sheet material comprised of a layer of copper and a stabilization layer on a surface of the copper. The stabilization layer is comprised of zinc oxide, chromium oxide, nickel oxide or a combination thereof and has a thickness between about 5 xc3x85 and about 70 xc3x85. A vapor deposited metal is provided on the stabilized layer.
It is an object of the present invention to provide a chromium coated copper layer for use in manufacturing printed circuit boards.
Another object of the present invention is to provide a method of forming a chromium coated copper layer as described above by a vacuum deposition process that does not require an extensive, rigorous pre-cleaning of the copper surface prior to deposition of the chromium.
Another object of the present invention is to provide a method of vacuum depositing a metal onto a copper surface.
A still further object of the present invention is to provide a generally continuous process as described above.
These and other objects will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims.